A fuel reformer is a device that transforms one type of fuel into another type of fuel. A common type of fuel reformer is a hydrogen fuel reformer which transforms fuel (e.g., natural gas, methane, liquid petroleum gas, etc.) into hydrogen. In a hydrogen fuel reformer, methane (CH4) or natural gas may react with water and oxygen at high temperatures (e.g., about 700° C. to about 1100° C.) to produce hydrogen (H2), carbon monoxide (CO), and other products. Fuel reformers may be used to produce hydrogen for fuel cell applications, or to provide a reducing atmosphere for catalyst regeneration in exhaust aftertreatment systems. In another use, fuel reforming may supply hydrogen gas to combustion chambers to facilitate and stabilize combustion under lean burn conditions (i.e., in an excess of air). In particular, because hydrogen ignites readily due to its high flame propagation speed, it may facilitate ignition of fuel and air in the combustion chamber.
Due to the high operating temperatures of hydrogen fuel reformers, the hydrogen-containing effluent gas leaving a hydrogen fuel reformer may be at high temperatures in a range of about 600° C. to about 800° C. or more. Prior to introduction of the reformed gas to an intake manifold and/or fuel admission valves for supporting lean burn combustion, the effluent gas should be sufficiently cooled to prevent shock issues in the combustion chamber. Ideally, the temperature of the effluent gas from a fuel reformer should be reduced to below about 120° C. prior to introduction into the combustion chamber. Coolers may be used for this purpose. However, it may be a technical challenge for a typical engine cooler or an industry cooler to withstand a hydrogen-rich environment due to hydrogen embrittlement.
Hydrogen embrittlement is caused by the diffusion of hydrogen atoms into a metal. The hydrogen atoms within the metal may recombine to form hydrogen molecules or other compounds that may create pressure within the metal. This pressure may increase to levels where the metal has reduced ductility, toughness, and tensile strength, such that the metal may eventually fracture or crack. Certain metals, such as steel, titanium, and aluminum alloys, are particularly vulnerable to hydrogen embrittlement compared to other types of metals and materials. As many coolers may include a steel framework, such coolers are vulnerable to hydrogen embrittlement. This problem may be further exacerbated by the high temperature of the effluent gas, as hydrogen diffusion into materials occurs more rapidly at higher temperatures. Hydrogen diffusion into the framework of the cooler may be further assisted by a hydrogen concentration gradient between the framework of the cooler and the effluent gas. Some coolers do not purge the gaseous mixture in the cooler at shutdown, such that hydrogen diffusion into the metal framework may occur at even lower temperatures due to significantly more hydrogen outside the metal than inside. Accordingly, coolers may be susceptible to early failure due to hydrogen embrittlement when used to cool hydrogen-containing effluent gas from fuel reformers.
U.S. Pat. No. 8,852,820 discloses a hydrogen fuel cell module having heat exchangers that heat fuel and air inlet streams, wherein the housing of the module is coated with an anti-hydrogen embrittlement material that protects the module from hydrogen embrittlement. While effective, the patent does relate to coolers for cooling effluent gas from fuel reformers. Thus, there is a need for improved cooler designs for cooling hydrogen-containing effluent gas from fuel reformers.